Langerin is a pathogen recognition receptor of the innate immune system and plays an important role in regulating the immune response. It binds the carbohydrate layer (glycocalyx) on the pathogen surface. The key element in this process is a central Ca2+ ion coordinated by a cage of charged amino acid side in the carbohydrate recognition domain which mediates the binding and release of pathogens. In collaboration with the group of Dr. Christoph Rademacher (MPI of Colloids and Interface, Potsdam) we could show that an intra-domain allosteric network modulates the Ca2+-affinity in Langerin which in turn determines the carbohydrate affinity.